U.S. Homeland Security Secretary Jeh Johnson said on Wednesday that his department has been consulting social media as part of the process of conferring immigration benefits since early this year.

The Department of Homeland Security has been criticized over reports it did not routinely consult social media during the vetting process for visa applications and has not been doing enough to weed out potential attackers.

One of the shooters in the Dec. 2 killings of 14 people in San Bernardino, California, Tashfeen Malik, entered the United States on a K1 or "fiancee" visa. The Los Angeles Times has reported she had pledged her support to Islamic jihad in a private Facebook posting.

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Monitoring of social media as a way to identify potentially violent extremists was a hot-button issue in Tuesday's Republican presidential debate.

Johnson said his department began consulting social media early this year before granting certain immigration benefits but did not specify which ones.

"We had policies in place regarding consulting social media which in my judgment, particularly in this current environment, were too restrictive," Johnson told reporters at the unveiling of a revamped terrorism alert system.

"Under my leadership as secretary, we in fact began to consult social media in connection with conferring various immigration benefits and we will be doing more of this," he added. "Any reports or partial reports to the contrary are simply false."

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He noted DHS consults intelligence community databases and law enforcement databases when it does vetting for "a lot" of immigration benefits but said social media is also useful.

"There are some legal limits to what we can do," Johnson said. "But consulting social media is something that since I've been secretary I believe that we need to do and we have begun that."